1. Field of the Invention
The present invention relates to an etching process. More particularly, the present invention relates to a metal etching process and rework method thereof.
2. Description of Related Art
At present, there are two major etching techniques that are commonly used in the fabrication of semiconductor device, the wet etching process and the dry etching process. Wet etching process relies on chemical reaction to etch the film layers. On the other hand, dry etching process relies on physical action to etch the film layers.
In general, a photoresist layer is formed over the need-to-be-etched layer prior to performing either a wet etching or a dry etching operation. Then, a photolithographic process is carried out to imprint the required pattern to the photoresist layer. Thereafter, the need-to-be-etched layer is etched using the photoresist layer as an etching mask. After that, the photoresist layer is removed. The most commonly used method for removing the photoresist layer includes using a plasma etching process. However, in the metal etching process for etching aluminum-copper alloy layers, the plasma process of removing the photoresist layer often produces a number of problems.
FIGS. 1A through 1C are schematic cross-sectional views showing the steps in a conventional metal etching process. First, as shown in FIG. 1A, a dielectric layer 102, a barrier layer 104, an aluminum-copper alloy layer 106, a protective layer 108, a hard mask layer 110 and a patterned photoresist layer 112 are sequentially formed over a substrate 100.
Next, as shown in FIG. 1B, an etching operation is carried out using the patterned photoresist layer 112 as an etching mask so that the pattern on the patterned photoresist layer 112 is transferred to the hard mask layer 110a. Thereafter, plasma is used to remove the patterned photoresist layer 112. However, using plasma to remove the patterned photoresist layer 112 requires a temperature around 180° C. At this temperature, the aluminum-copper alloy layer 106 will produce some metal precipitate (CuAl2) near the junction between the bottom of the alloy layer 106 and the barrier layer 104 and the metal precipitate will gradually migrate toward the barrier layer 104.
As shown in FIG. 1C, using the patterned hard mask layer 110a as a mask, the aluminum-copper alloy layer 106 is etched. Due to the effect of the metal precipitate 107 in the barrier layer 104, an incomplete removal (indicated as area 10) of the barrier layer 104 occurs. Thus, the phenomenon of conduction in the metallic layer of the semiconductor device will occur leading to a short circuit. Furthermore, due to the presence of the metal precipitate 107, the gaseous etchant will move toward the sidewalls of the aluminum-copper alloy layer 106 in the process of patterning the aluminum-copper alloy layer 106 leading to over-etching problem.
The foregoing problems can be largely resolved by lowering the temperature for removing the patterned photoresist layer and increasing the time for etching the aluminum-copper alloy layer. Yet, lowering the temperature for removing the patterned photoresist layer frequently lead to an incomplete removal of the photoresist material and needs a longer removing period. The longer removing period also increases the production of metal precipitate and escalates the aforementioned metal short circuit problem. On the other hand, increasing the etching time for the aluminum-copper alloy layer may damage the hard mask layer leading to the exposure of the aluminum-copper alloy layer.